The present invention relates generally to the treatment of end stage renal disease. More specifically, the present invention relates to methods and apparatus for performing peritoneal dialysis.
Using dialysis to support a patient whose renal function has decreased to the point where the kidneys no longer sufficiently function is known. Two principal dialysis methods are utilized: hemodialysis and peritoneal dialysis.
In hemodialysis, the patient's blood is passed through an artificial kidney dialysis machine. A membrane in the machine acts as an artificial kidney for cleansing the blood. Because it is an extracorporeal treatment that requires special machinery, certain inherent disadvantages exist with hemodialysis.
To overcome the disadvantages associated with hemodialysis, peritoneal dialysis was developed. Peritoneal dialysis utilizes the patient's own peritoneum as a semi-permeable membrane. The peritoneum is a membranous lining of the abdominal body cavity. Due to good perfusion, the peritoneum is capable of acting as a natural semi-permeable membrane.
Peritoneal dialysis periodically infuses sterile aqueous solution into the peritoneal cavity. This solution is called peritoneal dialysis solution, or dialysate. Diffusive and osmotic exchanges take place between the solution and the blood stream across the natural body membranes. These exchanges remove the waste products that the kidneys normally excrete. The waste products typically consist of solutes like urea and creatinine. The kidneys also maintain the levels of other substances such as sodium and water which need to be regulated by dialysis. The diffusion of water across the peritoneal membrane during dialysis is called ultrafiltration.
In continuous ambulatory peritoneal dialysis, a dialysis solution is introduced into the peritoneal cavity utilizing a catheter. An exchange of solutes between the dialysate and the blood is achieved by diffusion. Further removal is achieved by providing a suitable osmotic gradient from the blood to the dialysate to permit water outflow from the blood. This allows a proper acid-base, electrolyte and fluid balance to be achieved in the body. The dialysis solution is simply drained from the body cavity through the catheter.
Peritoneal dialysis raises a number of concerns including: the danger of peritonitis; a lower efficiency and therefore increased duration of dialysis hours compared to hemodialysis; and costs incurred when automated equipment is utilized.
A number of variations on peritoneal dialysis have been explored. One such variation is automated peritoneal dialysis ("APD"). APD uses a machine, called a cycler, to automatically infuse, dwell, and drain peritoneal dialysis solution to and from the patient's peritoneal cavity. APD is particularly attractive to a peritoneal dialysis patient, because it can be performed at night while the patient is asleep. This frees the patient from the day-to-day demands of continuous ambulatory peritoneal dialysis during his/her waking and working hours.
The APD sequence typically lasts for several hours. It often begins with an initial drain cycle to empty the peritoneal cavity of spent dialysate. The APD sequence then proceeds through a succession of fill, dwell, and drain phases that follow one after the other. Each fill/dwell/drain sequence is called a cycle. APD can be and is practiced in a number of different ways.
Continuous cycling peritoneal dialysis ("CCPD") is one commonly used APD modality. During each fill/dwell/drain phase of CCPD, the cycler infuses a prescribed volume of dialysate. After a prescribed dwell period, the cycler completely drains the liquid volume from the patient, leaving the peritoneal cavity empty or "dry." Typically, CCPD employs six fill/dwell/drain cycles to achieve a prescribed therapy volume.
After the last prescribed fill/dwell/drain cycle in CCPD, the cycler infuses a final fill volume. The final volume dwells in the patient through the day. It is drained at the outset of the next CCPD session in the evening. The final fill volume can contain a different concentration of dextrose than the fill volume of the successive CCPD fill/dwell/drain fill cycles the cycler provides.
Tidal peritoneal dialysis ("TPD") is another APD modality. Like CCPD, TPD includes a series of fill/dwell/drain cycles. Unlike CCPD, TPD does not completely drain dialysate from the peritoneal cavity during each drain phase. Instead, TPD establishes a base fill volume during the first fill phase and drains only a portion of this volume during the first drain phase. Subsequent fill and drain cycles infuse, then drain a small tidal volume under the base volume, except for the last drain phase. The last drain phase removes all dialysate from the peritoneal cavity.
Yet another variation of automated peritoneal dialysis is reciprocating peritoneal dialysis ("RPD") and/or semi-continuous peritoneal dialysis. In such systems, dialysis solution is infused into the peritoneal cavity and then, typically, on a continuous process basis a portion of the dialysis solution is sequentially drained, cleansed, and reinfused.
FIG. 1 illustrates a system of semi-continuous dialysis. The system was outlined by Di Paolo in "Acceleration of Peritoneal Dialysis With Single Device", 19 Nephron 271-277 (1977). A single needle 10 is used to infuse fluid from the sterile reservoirs 12, 14 into the patient where it dwells and then subsequently flows to drain 16. Inflow into the patient is achieved through a pump 18, while outflow is achieved by gravity.
U.S. Pat. No. 4,190,047 discloses a single catheter system that utilizes two pumps to alternate inflow and outflow of dialysate fluid. During the outflow cycle, fluid is passed through the blood path of the dialyzer where it is "cleaned" prior to the next inflow.
FIG. 2 sets forth a figure from U.S. Pat. No. 5,141,493. FIG. 2 illustrates the three loop system of the '493 patent wherein dialysate is reciprocated into and out of the patient using a reversible pump (first loop) into a second loop. In the second loop, the dialysate passes through a dialyzer being regenerated by non-sterile dialysate flowing in the third loop. The difference between the '493 system and the earlier systems is that both regeneration and reciprocation are continuous.
All of the above investigators have reported increased small molecule clearance and high ultrafiltration with either a continuous flow or reciprocating type systems. Naturally, an advantage of this type is desirable. However, these prior systems are quite complex in their operation, set-up, and control. Therefore, a need exists for an improved peritoneal dialysis system based on a reciprocating and/or semi-continuous peritoneal dialysis.